1. Field
The present invention relates to the field of pulsed lasers, and more particularly to pulsed lasers used for holography.
2. Art Background
Lasers have been utilized in many engineering and scientific applications for a variety of purposes. For example, lasers may be used as an optical "stylus" for playing pre-recorded television presentations on plastic disks similar to phonograph records, or may be used in military applications such as laser-directed bombs and anti-missile weapons. Another promising use of lasers is in the field of wave front reconstruction, frequently referred to as holography. Holography provides a scientist with a means for recreating images such that the images appear to originate from an actual object. Holography has found application in a number of areas, such as the high accuracy measurement of an object's dimensions, the "freezing" of short lived processes such as particulate combustion, holographic interferometry, holographic optical memories, as well as numerous other terrestrial and space applications.
In general, a holographic recording system includes a laser light source having of a particular wavelength, which is split by a beam splitter such that two beams are provided. One beam, the reference beam, is passed directly to a recording medium such as a photographic plate. The other beam, referred to as the object beam, is used to irradiate the target object which is the subject of the hologram. The radiation comprising the object beam is scattered and dispersed such that some of the incident radiation interferes with the reference beam on the recording medium. By appropriate processing, an image of the target object can be reconstructed and viewed from different angles and elevations, such that a three-dimensional effect is obtained.
Ruby lasers, which provide an instantaneous laser pulse, are the dominant light source in pulsed laser holography. The use of a pulsed laser permits the "freezing" of high speed events, such as combustion processes. Unfortunately, existing ruby lasers which are used for holographic purposes, are adaptations of lasers designed for other uses such as welding. A typical ruby laser rod has a diameter of six to ten millimeters. In order to provide TEM.sub.00 operation, one must aperture the rod cavity to a diameter of one or two millimeters, which results in a one to two order of magnitude power reduction. Thus, a substantial portion of the ruby rod remains unused in existing holographic imaging systems. By providing appropriate tuning elements, such as etalons, satisfactory laser emissions may be produced by the ruby rod for holographic purposes. However, proper tuning of etalons on either side of the ruby rod is typically complex and involved, and requires a temperature controlled environment in order to minimize thermal induced variations in the optical tuning elements.
Accordingly, there exists a need to provide a means for increasing the total usable energy of a pulse laser for holographic purposes, and simplifying the tuning of the laser output to provide higher quality holographic images. As will be disclosed below, the present invention utilizes a retro-reflecting roof mirror in conjunction with a transverse mode selector in order to provide a folded cavity within the lasing medium to be utilized. Thus, the present invention provides multiple identical beams which may be directly used in holographic systems, thereby eliminating the need for beam splitting. The use of a retro-reflecting roof mirror in conjunction with a transverse mode selector permits numerous variations in the total cavity length, laser energy output, and wavelength.